Varying Patterns of Speciation Essay -- Wallaces Line Plate Tectonics

Varying Patterns of Speciation Wallace’s line, located in the Malay-Archipelago, is one of the best known and most studied boundaries of zoogeography in the world. It is a transition zone between the islands of Borneo and Sulawesi and the islands of Bali and Lombork, which marks both the convergence and division of the diverse flora and fauna found in the Asian (Borneo, The Philippines, and Western Indonesia), and the Australian regions (Sulawesi, Eastern Indonesia, Australia, and New Guinea) (Schulte 2003). The hypothetical line was first proposed by Alfred Russel Wallace in 1858 after observing many morphological differences of various bird species in the Asian and Australian regions (Raven 1935). In the past, to confirm the placement of Wallace’s hypothetical line, researchers have applied the theories of plate tectonics and continental drift in order to create geographical reconstructions of land masses. From this information, researchers were able to substantiate a majority of the boundaries of the originally drawn line. Presently, however, due to the enigmas found on the island of Sulawesi, a portion of the line between Borneo and Sulawesi (Celebes) still remains uncertain (Whitmore 1981). Researchers have identified two genera that contradict the location of the line: the macaque monkey (Macaca species) and the Sulawesi toad (Bufa celebensis) (Evans et al. 1998). Whereas geographical phenomena such as tectonic plate shifts, rising and falling sea levels, and climatic fluctuations have caused the morphology of the Sulawesi toad to remain fairly undifferentiated, the ancestral macaque monkeys have evolved into seven distinct endemic species. The zoogeography on the eastern and western sides of Wallace’s line... ...esi. Evolution. 57:6:1436-1443. Evans, Ben J., Juan Carlos Morales, Jatna Supriatna, and Don J. Melnick. 1998. Origin of the Sulawesi Macaques (Cercopithecidae: Macaca) as Suggested by mitochondrial DNA phylogeny. Biological Journal of the Linnean Society. 66:539-560. Michaux, B. Land Movements and animal distributions in east Wallacea (eastern Indonesia, Papua New Guinea and Melanesia). Palaeogeography, Palaeoclimatology, Palaeoecology. 112:323-343. Raven, Henry C. 1935. Wallace’s Line and the Distribution of Indo-Australian Mammals. New York. Schulte, James A. II. Jane Melville, and Allan Larson. 2003. Molecular phylogenetic evidence for ancient divergence of lizard taxa on either side of Wallace’s Line. The Royal Society. 270:597-603. Whitmore, T.C. 1981. Wallace’s Line and Plate Tectonics. Clarendon Press. Oxford University Press, New York.